The use of wood burning stoves is very common particularly in those areas where wood logs can be secured fairly inexpensively. In urban areas, the use of wood as an energy source is not as popular because the cost of wood is high and also because the use of wood logs is considered by many to be an annoyance requiring constant cleaning of the area around the heating unit and the need to constantly bring the wood logs to the unit. Also, the problems involving creosote build-up and the release of hydrocarbon pollutants into the atmosphere have dissuaded many people away from the use of wood or coal as an energy source.
To overcome the aforementioned problems, attempts have been made to develop heating units that would burn a cleaner, easier to handle fuel such as wood pellets. The concept was that the pellets could be packaged in a bag and readily purchased at a neighborhood store. The heating units had a hopper that would hold a large supply of the pellets and the pellets would be automatically fed into the burner thereby relieving the user of the need to constantly move logs into the heating unit. U.S. Pat. Nos. 4,513,671 and 4,517,903 show pelletized wood furnaces.
The wood pellet heating unit has not met with a great deal of success for several reasons. The supply of the fuel source is dependent upon a limited number of producers and many potential users may have concerns of having a readily available supply. Also, the heating units have not been as efficient with respect to the fuel burning and the heat output as the more typical wood log heating units. One technical problem is with the methods of providing air for the fuel. Most pellet heating units use a blower to move outside air, either from the area surrounding the unit or from the outside of the building, into the burner portion of the heating unit. If the blower is located upstream of the burner, the unit is said to be positive pressure since the firebox will have a pressure greater than atmospheric. U.S. Pat. No. 4,517,903 is a positive pressure system since the blower is located in the fuel burner and the combustion air is pushed into the burner area. U.S. Pat. No. 4,513,671 is a negative pressure system since the blower is located beyond the fuel burner and the combustion air is essentially sucked into the burner with the firebox having a pressure slightly less than atmospheric.
The use of either positive or negative pressure presents several problems that may contribute to lack of acceptance of the pellet heating units. With the positive pressure unit, the firebox is under pressure so that when the door or other access to the firebox is opened, smoke and other matter will be pushed into the room. In the negative pressure unit, there is a tendency for the blower to clog from the particulate material in the exhaust gases and also a considerable amount of heat is sucked out of the heating unit into the exhaust pipe tending to generate a fairly high temperature at the exhaust pipe.
Attempts have been made to provide both a positive and negative pressure distribution in a firebox. For example, U.S. Pat. No. 1,604,271 to Friedman provides this in a furnace by splitting intake air into two streams, one directed through the grate of the firebox, and the other to the combustion exhaust stream to create a draft in the exhaust.
Thus there exists a need for a pellet fuel heating unit that can overcome all of the aforementioned problems. An object of this invention is to provide a heating unit having a balanced pressure system that will not only burn wood pellets but will burn a pellet-like fuel that is readily available, will burn cleaner than wood pellets, and is inexpensive, namely, shelled corn or corn kernels. The use of corn kernels, primarily U.S. Department of Agriculture grades 1 through 3 feed corn, provides the user with an inexpensive, clean and readily available fuel. It is estimated that there are over 4 billion bushels of suitable feed corn in storage facilities throughout the country and the supply is growing daily.
As shelled corn or corn kernels require a high temperature in order to burn properly without, in essence, self-extinguishing, a highly turbulent combustion air flow to the fuel is required which encompasses each kernel. Thus, a further object of the invention is to provide a heating unit having a turbulent combustion air flow to the area in which the fuel is burned.
It is yet another object of this invention to provide a pellet fuel heating unit that uses both a negative and positive pressure system and avoids the problems associated with either type of system.
Another object of this invention is to provide a heating unit which reduces the fouling and discoloration of the heating unit firebox window.
Still another object of this invention is to provide a heating unit having a high heating efficiency and highly efficient combustion of the fuel.